The invention relates to a method for operating an internal combustion engine with a crankcase, a crankcase vent and an intake system.
Vehicles with modern internal combustion engines have a crankcase vent which prevents leakage of lubricants, preferably oil or lubricant vapors, into the environment. In the simplest case, the crankcase vent consists only of a tube or hose connection between the crankcase and an intake tube of the internal combustion engine, wherein the vacuum in the intake tube suctions lubricant vapors in the crankcase. Depending on the construction of the internal combustion engine and the lubricant circulation, the intake system constructed in this manner may also include a pressure control valve, a throttle or an auxiliary branch, for example disposed upstream of a damper flap of the internal combustion engine and/or a check valve which prevents an undesirable flow direction. It is known from online oil consumption measurement that internal combustion engines have high oil consumption in operating phases with low absolute intake tube pressure, corresponding to a very high intake tube vacuum. Such operating phases occur, for example, during deceleration, i.e., when the vehicle speed is reduced by way of the engine brake, for example when driving downhill. The increase of the oil consumption in these operating phases is mainly influenced by the large differential pressure between the intake tube pressure, i.e., the pressure in the intake system, and the pressure in the crankcase. For example, if a differential pressure of about 650 mbar is exceeded, a large increase in the oil consumption is observed. The oil consumption in the aforedescribed operating phases is typically optimized through improvements of piston rings and pistons, i.e., by improving the sealing of movable parts. However, this entails significantly more stringent requirements for precision and significant additional costs as well as increased friction losses of the sealing piston rings and pistons.
It is an object of the invention to provide a method for operating an internal combustion engine having a crankcase, a crankcase vent and an intake system, which obviates the aforementioned disadvantages and which significantly reduces the oil consumption in the aforementioned operating phases with zero load or in a deceleration phase without requiring modification of the pistons and/or the piston rings.